In conventional tunneling excavations of the kind referred to, when the tunneling machine reaches the vertical shaft, it has been necessary to have the tunneling machine advanced into the shaft after providing a hole in a retaining wall such as, for example, a sheet pile or concrete wall disposed along an inside wall of the vertical shaft. If the hole is made in the shaft wall, however, highly water containing soil or gushing water will flow out of the soft ground and, in order to prevent such risks, the ground layer adjacent the vertical shaft has been improved by applying auxiliary processes for preventing ground collapse and gushing water such as a chemical grouting impregnating process, CCP process, well point process, ground water freezing process or the like in advance of propelling the tunneling machine. Therefore, a considerable number of days and cost have been required to determine and perform a proper type of the auxiliary process depending on various conditions of the soft ground layer. However, such auxiliary process has been indispensable in the cases of making tunnels for public facilities or the like in a soft ground under cities or the like located at a very low level place or even below the sea level.